I've actually done more than a little outfitting for my "older" systems, namely software; plus a little hard ware. Mostly Wii, DS, 64, & Advance; in preparation for my possible forthcoming video game expenditure abstinence. Much of said outfitting was done online (Amazon). Always remember the golden rule: Buy from Amazon directly, or at the very least "Fulfillment By Amazon"; and always buy "New" whenever possible. Other than online; I've made some pretty great finds at used game stores as well, over the last year or so.
No matter where you go, there you are.